Did you know that the dahlia is the national flower of Mexico? It should not come as a surprise since the mountains of Mexico and Guatemala are considered the home of origin for today’s dahlia ancestors. 16th century Spanish conquistadors, while busy conquering the vast Aztec Indian nation, also made some interesting explorations-one of which was the collection of New World plant life. Botanist accompanying the soldiers discovered what is sometimes referred to as the treedahlia(D. imperialis). The flowers of this species were open-centered, single blooms with pendant stems. The hollow stems of these plants, some growing to over 20 feet, were often used for hauling water or as an actual source of water to traveling hunters. In fact the Aztec name for “tree dahlias” was acocotli or water-cane.
About 200 years passed before dahlia seeds, roots, and plants found their way to Europe. From the Royal Botanical Gardens in Madrid, Spain, dahlia seeds and tubers were soon sent throughout western Europe. Initial breeders of dahlias were more interested in it as a food source since the blooms were not particularly noteworthy. Perhaps, fortunately for us today, these experiments met with little success. By the early 18th century the first fully double forms began to emerge. From 1810 to 1840 dahlias were very popular as nurserymen continued to expand the combinations of colors in dahlias that were global in shape. Soon however, as is with many other breeding projects, it was felt that all combinations had been reached and the interest in dahlias began to wane.
In 1872 a box of dahlia roots were sent from Mexico to Holland. The impact of this long journey was devastating in that all but one tuber failed to make the crossing. This singular root, however, proved quite astonishing in that it produced a brilliant red bloom with petals that were rolled back and pointed! Immediately dahlias regained their place on the benches of plant breeders who began to successfully combine this new variety( D. juarezii) with parents of early varieties and their progenies have served as the parents of today’s hybrids.
Today there are numerous organizations throughout the world with the main goal of advancing the growing and advancement of dahlias. This Website is provided by the American Dahlia Society (ADS). There are sister organizations in such places as Great Britain, New Zealand and Australia as well as several other European and Asian countries.
The ADS categorizes today’s dahlias into various groups based on size, form and color. They are as follows:
AA -(Giant), over 10 inches in diameter
A -(Large), over 8 to 10 inches in diameter
B -(Medium), over 6 to 8 inches in diameter
BB -(Small), over 4 to 6 inches in diameter
M -(Miniature), up to 4 inches in diameter
BA -(Ball), over 3.5 inches in diameter
MB -(Miniature Ball), over 2 to 3.5 inches in diameter
P -(Pompon), up to 2 inches in diameter
MS -(Mignon Single), up to 2 inches in diameter
The definitions of form are simplified from those that appear in the ADS 2002 Classification and Handbook of Dahlias. They are therefore descriptive but not appropriate for judging criteria, for example. The mature petals that determine the size are also used to determine the form.
The 18 classifications of form recognized by the ADS are as follows:
Formal Decorative – Rayflorets (petals) are flat, partially revolute (petal edges roll back), or partially involute (petal edges roll forward). The petals are uniform and regularly arranged, tending to curve toward the stem.
Informal Decorative – Ray florets are twisted, or curled, or wavy creating an affect that the petals are not flat. The petals may be partially revolute with their arrangement appearing irregular.
Semi-Cactus – The ray florets are broad at the base, straight, incurved or recurved and the ray florets revolute for up to one half of their length.
Straight Cactus – The ray florets revolute for more that one half of their length; they also may be pointed, straight, or recurved, radiating in all directions from the center of the flower head.
Incurved Cactus – These dahlias also have ray florets that are curved for more than one half of the length but the pointed petals have a pronounced curvature toward the center of the flower head.
Laciniated – The split or laciniation should be in proportion to the ray floret length. There should be an overall twisting in the area of the split involute or revolute ray florets, to give an overall fringed effect.
Ball – fully double flowers, ball shaped or slightly flattened at the face, and the ray florets are blunt, rounded, or indented, involute for most of their length, fully involute for about one half their length, and normally displayed in a spiral arrangement.
Miniature Ball – Same form as ball dahlia , differing only in size.
Pompon – Fully double flowers similar to ball dahlias but more globular and smaller in size; also, the ray florets involute for their whole length and fully involute for more than half of their length.
Stellar – Fully double, breaking gradually from immature florets to fully developed outer florets. The outer florets should be narrow and involute with a slight recurve to the stem. The less mature florets should possess the same narrow and partially involute characteristic. The depth of the stellar dahlia type should be from one half to two thirds the diameter of the bloom, the greater depth being the ideal.
Waterlily – Fully double and symmetrical blooms with a side view that appears to be flat or saucer shaped. The ray florets are openly faced giving the bloom a delicate appearance. The center is closed and dome shaped breaking gradually to four to seven rows of fully developed outer ray florets which are also broad and slightly cupped.
Peony – An open centered dahlia with two or more rows of ray florets surrounding the discflowers(small tubular florets which make up the central part of the flower. Each has a pistil and stamens but generally no other conspicuous flower parts). Ray florets adjacent to the disc flowers may be smaller, twisted, and/or curled.
Anemone – Dahlias with one or more rows of ray florets surrounding a center of elongated tubular disc florets. These disc florets should be fully developed and present a domed, pincushion appearance.
Collarette – An opened faced dahlia with a single row of uniform evenly spaced compound ray florets in a flat plane surrounding the disc flowers. The petaloids that surround the disc are less than one-half the length of the ray florets.
Single – An open faced dahlia with a single row of uniform evenly spaced ray florets in a flat plane surrounding the disc flowers.
Mignon Single – Same as single, differing only in size.
Orchid – An open centered dahlia with a single row of evenly spaced ray florets in a flat plane surrounding the disc flowers. The ray florets are involute for 2/3s or more of their length and fully involute for at least 1/3 of their length.
Orchette – A bloom that combines the involute characteristics of the Orchid dahlia form with the petaloid characteristics of the collarette form.
Novelty Open – Dahlias with characteristics differing from the present classifications. These dahlias will have a disc center.
Novelty Fully Double – Dahlias with characteristics differing from the present classifications. These varieties will have a fully double center.
The ADS recognizes 15 different color or color combinations of dahlias. They are:
1) White 2) Yellow 3) Orange 4) Pink 5) Dark Pink 6) Red 7) Dark Red 8) Lavender 9) Purple and black 10) Light Blend – a blending of the lighter tints and tones of pink, yellow,lavender, and other pastels 11) Bronze 12) Flame 13) Dark Blend 14) Variegated – where two or more colors appear on the face of the bloom either in dots, splashes, stripes on narrow lines and 15) Bicolor – blooms with two distinctly clear and sharply separated color
– Brian Killingsworth, American Dahlia Society
Original article 1996, updated by Richard W. Peters 2002, updated by sharon Swaney 2018